Semiconductor processing chambers are used for depositing various material layers onto a substrate surface or surfaces. The processing chambers can be used for low-temperature processing, high-temperature processing, or a combination of both high- and low-temperature processing. One or more substrates or workpieces, such as silicon wafers, are placed on a workpiece support within the processing chamber. Both the substrate and workpiece support are heated to a desired temperature. In a typical chemical vapor deposition (“CVD”) processing step, reactant gases are passed over each heated substrate, whereby a CVD reaction deposits a thin layer of the reactant material in the reactant gases on the substrate surface(s). The processing may also include atomic layer deposition (“ALD”), plasma enhanced atomic layer deposition (“PEALD”), reduced pressure CVD (“RPCVD”), or any other process for depositing a thin layer of material onto a substrate. Through subsequent processes, these layers are made into integrated circuits, and tens to thousands or even millions of integrated devices, depending on the size of the substrate and the complexity of the circuits.
Various process parameters must be carefully controlled to ensure the high quality of the resulting deposited layers. One such critical parameter is the temperature of the substrate during each processing step. During CVD, for example, the deposition gases react at particular temperatures to deposit the thin layer on the substrate. If the temperature varies greatly across the surface of the substrate, the deposited layer could be uneven or have defects which may result in unusable areas on the surface of the finished substrate. Accordingly, it is important that the substrate temperature be stable and uniform while the reactant gases are introduced into the processing chamber.
Similarly, non-uniformity or instability of temperatures across a substrate during other thermal treatments can affect the uniformity of resulting structures on the surface of the substrate. Other processes for which temperature control can be critical include, but are not limited to, oxidation, nitridation, dopant diffusion, sputter depositions, photolithography, dry etching, plasma processes, and high temperature anneals.
Methods and systems are known for measuring the temperature at various locations near and immediately adjacent to the substrate being processed. Typically, thermocouples are disposed at various locations near the substrate being processed, and these thermocouples are operatively connected to a controller to assist in providing a more uniform temperature across the entire surface of the substrate. For example, U.S. Pat. No. 6,121,061 issued to Van Bilsen teaches a plurality of temperature sensors measuring the temperature at various points surrounding the substrate, including a thermocouple placed near the leading edge of the substrate, another near the trailing edge, one adjacent to a side of the substrate, and another below the substrate near the center of thereof.
Thermocouples used in semiconductor processing chambers typically have an elongated sheath to protect the thermocouple wires disposed therewithin from the gases and reactants introduced into the reaction chamber. The thermocouple typically also includes a support member that extends the length of the sheath and is configured to receive a pair of wires formed of dissimilar metals such that they form a thermocouple therebetween. The lifetime of the thermocouples is important in a semiconductor processing tool because a shorter lifetime requires more frequent down-time in an industry in which throughput, or the number of workpieces processed over a given time, is an important indicator of quality and cost of ownership of the entire tool. Accordingly, it is important that thermocouples are able to withstand cyclical changes in temperature as well as pressure. Typical issues that relate to shortened thermocouple lifetime include broken wires and inconsistent temperature measurement. The inconsistent temperature measurement of thermocouples may result from an inconsistent location of the junction of the wires (i.e., thermocouple junction) relative to the measuring tip of the sheath. When the location of the junction varies, the accuracy and consistency of the temperature measurement decreases. One example of when a thermocouple is considered to have failed is when the temperature measured is not accurate or is inconsistent from measurement to measurement. The reaction chamber must subsequently be shut down so that the failed thermocouple can be removed, and the tool down-time decreases profitability and increases cost of ownership of the tool. Accordingly, there is a need for a thermocouple design that provides a consistent position at which the junction is located to prevent the shifting of the junction relative to the sheath.